1. Field of the Invention
The present invention relates to a resin composition which excels in moldability, mechanical strength, impact strength, and the like. More particularly, the present invention concerns a molding material which is capable of satisfying requirements for high-level performance in use as structural members of automobiles, electrical appliances, etc. wherein improvements are made with respect to a decline in impact strength, which is generally liable to occur in a mixture of incompatible resins, without substantially impairing heat resistance and mechanical strength, i.e., the characteristic features of a polyphenylene ether resin, and moldability and organic solvent resistance, i.e., the characteristic features of a polypropylene resin by blending a polyphenylene ether resin, a polypropylene resin and a particular styrene monomer modified propylene copolymer.
2. Description of the Prior Art
It is well known that polyphenylene ether resins comprising phenylene groups having non-substituted or substituted rings, particularly poly-2,6-dimethyl-1,4phenylene ether, excel in heat resistance and mechanical strength and are useful as the so-called engineering resin, but that such polyphenylene ether resins also possess the undesirable property that their moldability is poor in injection molding or the like due to their high melt viscosities. In addition, their impact strength and solvent resistance as the heat-resistant engineering resin are still insufficient in many fields of application.
The idea is well known that, as an attempt in a case where desired various properties cannot be sufficiently satisfied by an individual resin material, insufficient properties are compensated for by blending that resin material with other resin materials. A material (U.S. Pat. No. 3,383,435) in which the moldability of a polyphenylene ether is improved by blending the polyphenylene ether with polystyrene which is compatible therewith and has good moldability has found widespread commercial use. With this material, however, both components have relatively poor resistance to organic solvents, and a blended composition thereof has insufficient solvent resistance. Since polypropylene resins excel in moldability, resistance to organic solvents and the like, have low specific gravities, and are low-priced, resins of this type are widely used for molded articles. However, their heat resistance is not very high, which is a drawback in their application as an engineering resin.
If a composition which has good properties of polyphenylene ether resin and polypropylene resin and is capable of compensating for undesirable aspects thereof can be obtained, it is possible to provide an excellent resin material having wide fields of application.
However, as can be understood in thermodynamic considerations of general polymer blends, since polyphenylene ether and polypropylene are incompatible and do not have affinity with each other, if the two components are simply mixed, the interface of the two-phase structure exhibited by the composition has poor adhesion. The two-phase interface of moldings obtained has low strength and therefore becomes a defective part, possibly resulting in a reduction in the mechanical strength and impact strength. In addition, the two phases are difficult to assume a form of uniform and fine dispersion, and delamination is liable to occur when it is subjected to shear stress at the time of molding such as injection molding.
Generally, one conceivable method for overcoming the above-described problems in a incompatible polymer blend is to compound a third component to a targeted two-component composition to improve the affinity. An agent which is called a compatibilizer is a typical example of the third component. Japanese Pat. Publication No. 7069/1967 discloses a composition in which a small amount of polyphenylene ether is mixed with polypropylene so as to improve the tension resistance and impact strength. However, this composition is insufficient to satisfy the harmony of the various properties which the present invention aims to attain. In addition, since improvements have not been essentially made on the affinity of the two components, it is difficult to cause excellent properties to be revealed by compounding a large quantity of polyphenylene ether. In the specification of U.S. Pat. No. 4,383,082, it is described that a block or radial teleblock copolymer of an alkenyl aromatic compound and a conjugated diene functions as a "compatibility imparting agent", and that polyolefin can be blended with polyphenylene ether uniformly at a considerably high ratio. However, no affinity improving agent effective for a combination of polypropylene resin and polyphenylene ether resin is suggested therein. In addition, although it is stated in Japanese Pat. Publication No. 22344/1981 that modified polypropylene is compounded with a polyphenylene ether. However, this reference merely discloses a method of preventing a decline in the mechanical strength occurring at the time when unmodified polypropylene is used by compounding one in which a styrene monomer is graft modified with polypropylene using organic peroxides.
The present inventors conducted research on improvements on a composition comprising a polyphenylene ether resin and a polypropylene resin so as to allow the composition to display the properties of the component resins, such as the heat resistance of the polyphenylene ether resin, the moldability and organic solvent resistance of the polypropylene resin, etc. with a good balance and to overcome a decline in the performance due to the poor affinity of two components, particularly the impact strength, which is a general demerit of the above-described incompatible blending materials.
As a result of the research, the present invention has been devised on the basis of the discovery that a propylene-dialkenylbenzene compound copolymer modified with an alkenyl aromatic monomer, obtained by allowing an alkenyl aromatic monomer and a polymerization initiator to coexist with a crystalline propylene-dialkenylbenzene compound copolymer, which is obtained by a copolymerization of propylene as a major component with a small quantity of dialkenylbenzene compound, is very effective as affinity improving agents for a composition comprising a polyphenylene ether resin and a polypropylene resin.